Heat sink

Lore & Background

Heat sinks transfer thermal energy from a higher-temperature device to a lower-temperature fluid medium, frequently air but also water, refrigerants, or oil. When the fluid medium is water, the heat sink is often called a cold plate. The design maximizes surface area in contact with the cooling medium, and factors such as air velocity, material choice, protrusion design, and surface treatment affect performance. Thermal adhesive or thermal paste fills air gaps between the heat sink and the device's heat spreader to improve efficiency.

Fourier's law of heat conduction governs the rate of heat transfer, and for a heat sink in a duct, conservation of energy and Newton's law of cooling yield equations relating air mass flow rate, specific heat capacity, and thermal resistance. A decrease in air flow increases the average air temperature and the heat sink's thermal resistance, raising the base temperature. Inlet air temperature strongly influences base temperature; recirculation of air within a product raises inlet temperature and thus base temperature. Without air flow, energy cannot be transferred. Natural convection requires free air flow over the heat sink; fins not aligned vertically or too closely spaced reduce efficiency.

Common materials include aluminium alloys (e.g., 1050, 6060, 6061, 6063) and copper. Aluminium alloy 1050 has high thermal conductivity (229 W/(m·K)) but is mechanically soft. Copper has roughly twice the thermal conductivity of aluminium (around 400 W/(m·K)) but is three times as dense, more expensive, and less ductile. One-piece aluminium heat sinks can be made by extrusion, casting, skiving, or milling; copper heat sinks can be made by skiving or milling, and sheet-metal fins can be soldered onto a copper body.

Reader's Guide

The heat sink is a fundamental component in thermal management of electronics, enabling reliable operation by preventing overheating. Its significance lies in its passive, simple design that relies on conduction, convection, and radiation to dissipate heat. The concept of thermal resistance simplifies selection: the total thermal resistance from the semiconductor die to ambient air is the sum of resistances from die to case, case to heat sink, and heat sink to ambient air. This allows calculation of die temperature rise given device dissipation. Manufacturers tabulate typical thermal resistance values for heat sinks and semiconductor devices, aiding commercial selection. However, the thermal resistance model is an approximation; it does not account for non-uniform heat distribution, temperature changes over time, or the non-linearity of radiation and convection with temperature rise. Despite these limitations, the heat sink remains essential for cooling CPUs, GPUs, power transistors, and LEDs, where component heat dissipation alone is insufficient. The choice of material—aluminium for cost and weight, copper for superior conductivity—and fin design directly impact cooling performance. The heat sink's legacy is as a ubiquitous, reliable solution for thermal regulation in countless electronic devices.

Did You Know?

• A heat sink is not a device with the 'magical ability to absorb heat like a sponge and send it off to a parallel universe'.
• Copper has around twice the thermal conductivity of aluminium, approximately 400 W/(m·K) for pure copper.
• Thermal resistance of a heat sink is expressed in degrees Celsius per watt (°C/W), analogous to electrical resistance.
• If there is no air flow around the heat sink, energy cannot be transferred.